122 HISTORY OF GEOLOGY AND PAL/EON TOLOGY. 



few reports that had been given by travellers merely con- 

 firmed the presence of volcanoes in one locality or another, 

 or mentioned the occurrence of the more striking varieties of 

 rock. 



Progress of Petrography Neptunists, Volcanists^ and Plu- 

 tonists. In the older mineralogical literature the rocks also 

 received a passing notice. As a rule, authors limited these 

 remarks to a description of their external features. Cronstedt 

 removed them from this subordinate position, and paved the 

 way for Werner's creative work in establishing the study of the 

 rocks as an independent branch of Geognosy. Werner's 

 classification and description of rock-varieties, published in 

 1786, comprised all existing knowledge of rocks, and replaced 

 the vague conceptions of former years by a series of exact 

 definitions and the introduction of a new, precise nomen- 

 clature. Werner distinguished simple and composite rocks ; 

 the former were discussed both as minerals and rock-forms, 

 e.g. quartz, gypsum, salt, etc., the latter were identified and 

 classified according to their mineralogical composition and 

 their age, e.g. granite, basalt, sandstone, marl, etc. 



Each rock was defined in respect of its texture, stratigraphical 

 position, jointing, age, origin, and occurrence. In the case of 

 composite rocks, the essential components were distinguished 

 from the accessory and the rock was classified solely upon the 

 ground of the essential components. 



The rapid advance of petrographical knowledge during the 

 first two decades of the nineteenth century was undoubtedly 

 the direct result of Werner's precise methods. All observers 

 during those decades gave marked attention to the determina- 

 tion of petrographical features. Saussure's descriptions of the 

 crystalline massive and schistose rocks in the Swiss Alps can 

 scarcely be surpassed. Monographs appeared from time to 

 time on special varieties of rock. Faujas de Saint-Fond, for 

 example, wrote a monograph on the "trap-rocks," in which he 

 showed how loosely this name had been applied in the litera- 

 ture, so that rocks of many different kinds were embraced 

 under it. 



Ferber and Dolomieu investigated the volcanic products of 

 Southern Italy. Desmarest, Faujas, and others examined the 

 Egyptian porphyries and so-called basalts. Leopold von 

 Buch introduced the name of gabbro^ and described leucite 



